|a|=|b|=2a与b的夹角为60度let a+b,a的夹角=x|a+b|^2 =|a|^2+|b|^2+ 2|a||b|cos60度=4+4+4=12|a+b|=2√3(a+b).a = |a+b||a|cosx|a|^2+ |a||b|cos60度+|b|^2 =|a+b||a|cosx6=4√3cosxcosx =√3/2x= π/6...